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Fast alpha transparency rendering method

  • US 5,923,333 A
  • Filed: 01/06/1997
  • Issued: 07/13/1999
  • Est. Priority Date: 01/06/1997
  • Status: Expired due to Term
First Claim
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1. A method for rendering opaque objects and transparent objects in at least one portion of a scene for graphic display in a computer system, said method comprising the steps of:

  • (a) rasterizing primitives of said opaque objects and sending depth values for pixels of said rasterized primitives to a z-buffer and sending image data for said pixels of said rasterized primitives to a frame buffer in said computer system;

    (b) processing primitives of said transparent objects, said processing comprising the steps of(b1) disabling writes to said z-buffer,(b2) culling all front-facing primitives of said transparent objects,(b3) rasterizing all back-facing primitives of said transparent objects to yield back-facing primitive pixels, and culling all said back-facing primitive pixels when depth values of said back-facing primitive pixels indicate that said back-facing primitive pixels are located behind at least one of said opaque objects, and(b4) alpha blending image data of remaining back-facing primitives with said image data in said frame buffer, and sending said alpha blended image data of said remaining back-facing primitives to said frame buffer, and(c) processing said primitives of said transparent objects, said processing comprising the steps of(c1) disabling writes to said z-buffer,(c2) culling said back-facing primitives of said transparent objects,(c3) rasterizing all front-facing primitives of said transparent objects to yield front-facing primitive pixels, and culling all said front-facing primitive pixels when depth values of said front-facing primitive pixels indicate that said front-facing primitive pixels are located behind at least one of said opaque objects, and(c4) alpha blending image data of remaining front-facing primitives with said image data in said frame buffer, and sending said alpha blended image data of said remaining front-facing primitives to said frame buffer.

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